1. Field of the Invention
The present invention is directed to a method for manufacturing a semiconductor wafer which is coated on one side and provided with a finish.
2. The Prior Art
Treatment which produces a finish on a semiconductor wafer is understood as material-removing treatment by means of which the shaping of the semiconductor wafer is essentially concluded. This treatment has the objective of transforming the surface of the semiconductor wafer, in particular the two sides of the semiconductor wafer, into a particularly flat, smooth and defect-free state. Such a treatment is particularly necessary to give the semiconductor wafer the properties which are required for further processing to form highly integrated electronic components. The most important treatment methods which produce a finish on the sides of a semiconductor wafer comprise material-removing methods such as chemical/mechanical polishing and fine grinding. In both cases, processing tools are used which have rotating working surfaces and act on one or both sides of a semiconductor wafer, specific removal of material being produced. In the case of chemical/mechanical polishing, a polishing means and a polishing cloth, which is stretched over the working surface of the processing tool (polishing plate) bring about the removal of material. In the case of fine grinding, the working surface of the processing tool is fitted with disks which have a material-removing layer of bound, fine grinding powder. Since every semiconductor wafer has a front side and a rear side, a distinction is made between a single-side treatment and a double-sided treatment. This distinction is explained below with reference to the example of polishing.
In the case of single-side polishing (SSP), after the rear side of the semiconductor wafer has been mounted on a suitable carrier only the front side of the semiconductor wafer is polished with a polishing cloth which is stretched over a polishing plate. During the mounting, a positively and frictionally engaging connection is produced between the rear side and the carrier, for example by means of adhesion ("template polishing"), bonding, cementing or vacuum application. Single-side polishing methods and devices are customary for single-wafer treatment ("single-wafer polishing") or for the treatment of groups of wafers ("batch polishing"). In the case of double-sided polishing (DSP), the front side and rear side of the semiconductor wafer are polished simultaneously. DSP occurs by leading a plurality of semiconductor wafers between two upper and lower polishing plates which have polishing cloths stretched over them. In this case, the semiconductor wafers are used in thin carrying cages ("wafer carrier") which are referred to as rotor wafers and are also used in a similar form when lapping semiconductor wafers. Double-sided polishing methods and devices are always configured for the treatment of groups of semiconductor wafers ("batch polishing").
A semiconductor wafer which is polished on both sides has very many fewer disruptive particles in comparison with a semiconductor wafer which is polished on only one side. Also, it is easier to clean and is less susceptible to contamination, and finally it can be metrologically measured, characterized and specified more easily.
U.S. Pat. No. 5,389,579 describes a method which indicates how a semiconductor wafer which is polished on one side can be manufactured by double-sided polishing.
Basically, a semiconductor wafer which is polished on both sides can be manufactured by polishing the front side and rear side successively with a single-side polishing method (sequential SSP). However, double-sided polishing is the method predominantly used to achieve polishing of both sides of a semiconductor wafer. Advantages of DSP over sequential SSP lie in the superior degree of flatness and plane-parallelism of the sides which can be achieved. Other advantages include the possibility of carrying out the polishing more cost-effectively and the higher throughput rate and the higher yield due to the elimination of the mounting, removal and turning steps necessary with sequential SSP.
A differentiation which corresponds to the difference between SSP and DSP can also be made with respect to fine grinding. In this case, it is also appropriate that the result of a fine grinding which is performed on one side even if both sides of a semiconductor wafer are successively ground, is inferior to the result of a fine grinding performed on two sides. The term "double-sided treatment" is used below for treatments of a semiconductor wafer which remove material, and produce a double-sided finish. This term is also used for double-sided polishing or for double-sided fine grinding, and is suitable for providing a semiconductor wafer with particularly flat, plane-parallel, smooth and defect-free sides. Such double-sided treatments have in common the fact that the semiconductor wafer is moved between rotating working surfaces of a processing tool. This causes material to be removed from the sides of the semiconductor wafer with the assistance of this tool.
Any method of handling an already polished or finely-ground semiconductor wafer with a mechanically acting handling tool runs the risk of causing damage to the wafer. For example, a handler entails the risk of damage to the polished or finely-ground surface of the disk, for example as a result of the fact that marks or scratches are produced. Such damage which relates to the side of the semiconductor wafer on which the electronic components are to be accommodated is particularly critical. On the other hand, there is a series of applications in which one side of the semiconductor wafer has to be coated at least once. This procedure then inevitably entails the risk of mechanical damage to the opposite side.
EP-607,940 A2 describes a method in which firstly there is a protective layer produced on the rear side of a semiconductor wafer and then the opposite front side of the semiconductor wafer is polished. However, the chronological arrangement of a single-side coating before single-side polishing has disadvantages. For example, single-side polishing is inferior to double-sided polishing in terms of the flatness and plane-parallelism of the sides which can be achieved. It is particularly disadvantageous that the surface of the side which is provided for coating and whose flatness is still inadequate is buried and conserved by a coating which precedes the polishing. Subsequent single-side polishing cannot eliminate this deficiency.